The present invention relates to absorption refrigeration systems and, more particularly, relates to heat exchanger bypass systems for absorption refrigeration systems.
In an absorption refrigeration machine, relatively cool, weak absorbent solution is usually pumped from an absorber to a generator where heat is provided to boil off refrigerant from the weak absorbent solution to form relatively strong absorbent solution. The relatively hot, strong absorbent solution formed in the generator is returned to the absorber where it is cooled and brought into contact with refrigerant vapor to form the relatively weak absorbent solution which is pumped back to the generator to begin the cycle again. Conventionally, in order to improve the efficiency of an absorption refrigeration machine, a heat exchanger is provided for transferring heat between the relatively hot, strong solution flowing from the generator to the absorber and the relatively cool, weak solution pumped from the absorber to the generator. The heat exchanger serves to preheat the solution which is to be heated in the generator and serves to precool the solution which is to be cooled in the absorber.
Occasionally, difficulty is experienced in absorption refrigeration machines of the type described above due to cooling of the strong absorbent solution in the heat exchanger below the solidification point of the solution. This may occur, for example, if too much heat is supplied to the generator or if cooling water supplied to the absorber is unexpectedly cold. When solidification of strong absorbent solution occurs in the heat exchanger, the heat exchanger is blocked and strong solution is prevented from flowing to the absorber from the generator. This may result in weak solution being overcooled in the absorber which, in turn, results in further solidification of strong solution in the heat exchanger as overcooled, weak solution is passed through it to the generator. Eventually, the level of solution in the absorber may be lowered to a level such that the solution pump, which forwards weak solution to the generator from the absorber, may run dry thereby damaging the pump. In addition, the strong solution in the generator may rise to a level at which the solution enters the condenser and flows into the evaporator thereby impairing operation of the refrigeration machine for a period of time even after the solution heat exchanger is desolidified.
In order to prevent solidification of strong solution in the heat exchanger from rendering the refrigeration machine totally inoperative, a heat exchanger bypass system may be provided for passing excess solution from the generator around the solution heat exchanger to the absorber. This permits the refrigeration system to operate, at least at partial capacity and efficiency, when the solution heat exchanger is blocked. Also, use of such a bypass system prevents excess solution in the generator from entering the condenser and prevents running the solution pump dry. At the same time, the bypass system inhibits further solidification in the solution heat exchanger and tends to aid in desolidification because the weak absorbent solution from the absorber, which passes through the unblocked side of the heat exchanger, is warmed by the generator and then is returned directly to the absorber by the bypass system. This warms the weak absorbent solution in the absorber which, in turn, warms the blockage in the heat exchanger when the now warm weak absorbent solution flows back through the heat exchanger to the generator.
However, since the generator normally operates at a higher pressure than the absorber, a heat exchanger bypass system is normally provided with some means to prevent direct communication between these components during periods of normal operation of the refrigeration system. For example, a trap filled with liquid may be provided in the bypass system for maintaining the pressure difference between the generator and the absorber by providing a liquid vapor barrier in the trap which prevents refrigerant vapor in the generator from flowing to the absorber. Unfortunately, because refrigerant vapor from the generator is in direct contact with the liquid in the trap, some refrigerant vapor is continually absorbed by the liquid in the trap resulting in an efficiency loss for the refrigeration system. Also, past experience has demonstrated that, while a bypass system with a liquid trap is adequate to serve its intended function, once it has operated, strong solution which remains in the trap tends to be cooled during periods of nonuse of the bypass system, and solidification may take place in the trap. The operator of the normally functioning absorption refrigeration machine is unaware that solidification has taken place in the trap but when solidification again occurs in the solution heat exchanger, he finds that the bypass system is unable to serve its intended function because the trap is blocked with solidified absorbent solution. As shown in U.S. Pat. No. 3,206,947 to Bourne, et al., solidification of strong solution in the trap may be prevented by continuously supplying a metered quantity of relatively weak solution to the bypass system at a suitable point to dilute strong solution which may be in the trap of the bypass system. However, as shown in the Bourne, et al. patent, a special liquid line having a metering device is required to supply the weak solution to the bypass system.